Synergistic local anesthetic compositions

ABSTRACT

A local anesthetic composition comprising a mixture in a pharmaceutically acceptable carrier of a particular toxin, namely, tetrodotoxin or desoxytetrodotoxin, and another compound, generally a conventional local anesthetic compound or a similar compound having nerve-blocking properties.

This application is a division of application Ser. No. 369,302, filed June 12, 1973 (now U.S. Pat. No. 3,966,934), which application Ser. No. 369,302 is a continuation-in-part application of application Ser. No. 206,181, filed Dec. 8, 1971 (now abandoned), which application Ser. No. 206,181 is a continuation-in-part application of application Ser. No. 109,942, filed Jan. 26, 1971 (now abandoned).

The present invention relates to a novel anesthetic composition comprising a mixture of (1) tetrodotoxin or certain derivatives thereof and (2) another compound, generally a conventional local anesthetic compound, or a similar compound having nerve-blocking properties. The invention also relates to a process for preparing the novel anesthetic compositions and to their use for inducing anesthesia.

Toxins from marine sources of extraordinary potency have been known for many years. This application particularly concerns novel uses for tetrodotoxin.

Tetrodotoxin is obtained from the ovaries and eggs of several species of puffer fish of the suborder Gymnodontes. It is also found in certain species of California newts of the genus Taricha; and the toxin obtained from these species, known as tarichatoxin, is identical with tetrodotoxin. Tetrodotoxin has been purified, and its molecular structure is determined to be an amino perhydroquinazoline of the formula: ##STR1##

Tetrodotoxin and species in which it occurs are more fully described in Pharmacological Reviews, Vol. 18, No. 2, at pages 997-1049.

Experiments with isolated nerves have shown that tetrodotoxin behaves in a fundamentally different manner from local anesthetics such as procaine and cocaine. In a voltage-clamped giant axon from the squid or lobster, the latter agents reduce both inward initial sodium current and outward potassium current. With tetrodotoxin, however, inward sodium current can be reduced or even obliterated, while the outward potassium current is totally unaffected. There are few, if any, other substances in which this unique action has been established.

Tetrodotoxin has not found any practical use as an anesthetic. While the compound can be used to induce nerve blocks in laboratory animals, the anesthetic dose is slightly below the lethal dose, which precludes, as a practical matter the use of the compound as an anesthetic in its own right.

Quite surprisingly, combinations of tetrodotoxin with a local anesthetic compound have been found to possess unusual anesthetic properties. This is manifested most significantly in improved longevity of action of combinations of the toxin with local anesthetics. In these combinations, tetrodotoxin is used in concentrations below that which produces reliable nerve blocks, and well below the toxic level.

Investigation of a wide variety of local anesthetics has shown that the action of the foregoing toxin in increasing longevity of action is general. Local anesthetics may be classified by characteristic chemical type. Within each chemical type there may be unexplained variations of activity. However, in all cases investigated, each member of the groups investigated has behaved similarly when combined with the foregoing toxin. Specific classes of local anesthetics investigated include anesthetic compounds characterized by

(i) the aminoacylanilide group, such as lidocaine, prilocaine, bupivacaine, mepivacaine and related local anesthetic compounds having various substituents on the ring system or amine nitrogen;

The following three ester types (ii), (iii) and (iv):

(ii) the aminoalkyl benzoate group, such as procaine, chloroprocaine, propoxycaine, hexylcaine, tetracaine, cyclomethycaine, benoxinate, butacaine, proparacaine, and related local anesthetic compounds;

(iii) cocaine and related local anesthetic compounds;

(iv) the amino carbamate group such as diperodon and related local anesthetic compounds;

(v) the N-phenylamidine group, such as phenacaine and related local anesthetic compounds;

(vi) the N-aminoalkyl amide group, such as dibucaine and related local anesthetic compounds;

(vii) the aminoketone group, such as falicain, dyclonine and related local anesthetic compounds; and

(viii) the aminoether group, such as pramoxine, dimethisoquine, and related local anesthetic compounds.

In each of the foregoing classes of local anesthetic compounds representative members have been enumerated. The experimental data support the conclusion that the observed effect of the toxin tested of unexpectedly extending the duration of action extend to the other known local anesthetic compounds of these groups and to the obvious modifications of the local anesthetic compounds tested. It may also be anticipated in the light of these discoveries that the novel combinations of the present invention will permit the use of concentrations of conventional local anesthetics in concentrations below the concentrations normally employed clinically. Thereby toxic manifestations sometimes observed as side effects can be minimized.

The chemical structures of some of the foregoing compounds are: ##STR2##

Other local anesthetic compounds which may be used in combination with tetrodotoxin (TTX) are the aminoacyl anilides described in the following table.

                                      Table A                                      __________________________________________________________________________      ##STR3##                                                                      Compound            R     R.sup.1                                                                             R.sup.2                                                                             R.sup.3                                    __________________________________________________________________________     A 2-tert. Butylamino-                                                            2',6'-acetoxylidide                                                                              H     H    H    C(CH.sub.3).sub.3                          B 2-(N-n-Butyl-tert. butylamino)-                                                2',6'-acetoxylidide                                                                              H     H    n-C.sub.4 H.sub.9                                                                   C(CH.sub.3).sub.3                          C 2-(N-n-Propyl-tert. amylamino)-                                                2',6'-acetoxylidide                                                                              H     H    n-C.sub.3 H.sub.7                                                                   C(CH.sub.3).sub.2 C.sub.2 H.sub.5          D 2-tert. Butylamino-                                                            2',6'-propionoxylidide                                                                           H     CH.sub.3                                                                            H    C(CH.sub.3).sub.3                          E 2-(N-Ethyl-iso-propylamino)-                                                   2',6'-propionoxylidide                                                                           H     CH.sub.3                                                                            C.sub.2 H.sub.5                                                                     CH(CH.sub.3).sub.2                         F 2-Methylamino-4'-(n-butoxy)-                                                   2',6'-dimethylpropion-anilide                                                                    n-C.sub.4 H.sub.9 O                                                                  CH.sub.3                                                                            H    CH.sub.3                                   G 2-(N-Methyl-n-propylamino)-                                                    2',6'-butyroxylidide                                                                             H     C.sub.2 H.sub.5                                                                     CH.sub.3                                                                            n-C.sub.3 H.sub.7                          H 2-Dimethylamino-                                                               2',6'-acetoxylidide                                                                              H     H    CH.sub.3                                                                            CH.sub.3                                   J 2-Ethylamino-2',6'-                                                            acetoxylidide     H     H    H    C.sub.2 H.sub.5                            K 2-Cyclobutylamino-2',6'- acetoxylidide                                                           H     H    H                                                                                    ##STR4##                                  L 2-tert. Amylamino-                                                             2',6'-acetoxylidide                                                                              H     H    H    C(CH.sub.3).sub.2 C.sub.2 H.sub.5          M 2-(N-Methyl-n-butylamino)-                                                     2',6'-acetoxylidide                                                                              H     H    CH.sub.3                                                                            n-C.sub.4 H.sub.9                          P 2-(N-Ethyl-sec. butylamino)-                                                   2',6'-acetoxylidide                                                                              H     H    C.sub.2 H.sub.5                                                                     CH(CH.sub.3)C.sub.2 H.sub.5                Q 2-Amino-2',6'-propionoxylidide                                                                   H     CH.sub.3                                                                            H    H                                          S 2-(N-Ethyl-n-propylamino)-                                                     2',6'-butyroxylidide                                                                             H     C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                                                                     n-C.sub.3 H.sub.7                          T 2-Diethylamino-2',6'-                                                          valeroxylidide    H     n-C.sub.3 H.sub.7                                                                   C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                            __________________________________________________________________________

In the present invention the foregoing local anesthetics are used in a pharmaceutically acceptable carrier, such as water, water-ethanol, dextrose solutions, saline solution and blends thereof, in concentrations which are customarily used by physicians. Exemplary concentrations of local anesthetics having clinical application are:

    ______________________________________                                                            % by weight                                                 ______________________________________                                         lidocaine            0.5      --     5                                         prilocaine           0.5      --     5                                         procaine             0.5      --     5                                         tetracaine           0.1      --     1                                         bupivacaine          0.25     --     1                                         hexylcaine           0.5      --     2.5                                       2-[N-n-propyl-tert. amylamino]-                                                2',6'-acetoxylidide  0.1      --     2.0                                       2-[N-n-butyl-tert. butylamino]-                                                2',6'-acetoxylidide  0.1      --     2.0                                       ______________________________________                                    

As mentioned above, the present invention also may permit the use of the usual local anesthetics in a lower than normal concentration. For example, the combination of tetrodotoxin with lidocaine permits the latter to be used in a concentration of as little as 0.05 percent by weight.

The carrier additionally contains from 0.5 to 10, usually from 0.5 to 5, micrograms per milliliter of tetrodotoxin or from 10 to 20 micrograms per milliliter of desoxytetrodotoxin. In addition, the local anesthetic preparation may contain a vascoconstrictor, as is well known in the art, such as epinephrine, norepinephrine, phenylephrine and levonordephrine.

The local anesthetic compositions may be prepared by dissolving the local anesthetic compound, tetrodotoxin or derivative thereof and a vascoconstrictor, when present, in the carrier or in separate portions of the carrier which are thereafter blended together.

Application of the local anesthetic compositions is accomplished in the usual manner, i.e., by infiltration or injection.

EXAMPLE 1

Female Charles River rats, weighing between 100 and 200 grams, were used. There were 5 rats per group and each animal received 0.2 milliliters of drug solution in the right thigh. The injections were made in such a way as to deposit the solution around the sciatic nerve trunk close to the popliteal space. After being injected, each animal was examined at intervals to determine onset, depth, and duration of nerve block as manifested by impairment of motor function in the injected leg. Frequencies of (a) complete block, (b) partial block, and (c) slight effect on motor function were noted for each group of animals. Two end points for duration of block were used: recovery of the ability to grasp when placed on an inclined screen and complete recovery of motor function.

All solutions contained 1 to 100,000 parts epinephrine which was added immediately prior to use. All solutions were freshly prepared on the day of use.

The results are summarized in Tables I- III. Depression was occasionally noted, but there were no fatalities with these doses of tetrodotoxin.

Table I: At 1 μg/ml and 2 μg/ml tetrodotoxin produced no complete blocks. At 5 μg/ml, it produced complete blocks in all five injected. Mean onset time was about 20 minutes, and the blocks persisted for somewhere between 51/2 hours and 24 hours. All animals were completely recovered when examined 22 to 24 hours post injection. Because this concentration of tetrodotoxin by itself produced 100 percent frequency and blocks of such long duration, there are no differences, except in onset times, between the results obtained with it alone and those obtained with the tetrodotoxin-lidocaine combination. However, the combinations of 1 μg/ml and 2 μg/ml of tetrodotoxin with lidocaine clearly show durations of block that are markedly greater than those obtained with lidocaine alone.

                                      TABLE I                                      __________________________________________________________________________     RAT SCIATIC NERVE BLOCKS                                                                                      Duration (min.)                                        Concentration                                                                             Onset                                                                              Frequency                                                                               Mean ± S. D.                                  Compound                                                                              as Base                                                                               pH (min.)                                                                             C  P  S  C.R.    R.G.                                    __________________________________________________________________________     Tetrodotoxin                                                                          1 μg/ml                                                                             4.4                                                                               --  0/5                                                                               1/5                                                                               4/5                                                                               --      --                                             2 μg/ml                                                                             5.4                                                                               --  0/5                                                                               2/5                                                                               3/5                                                                               --      --                                             5 μg/ml                                                                             4.3                                                                               22  5/5                                                                               -- -- --      5.5<24 hrs                              Lidocaine                                                                             0.125%  5.1                                                                               8   5/5                                                                               -- --  85 ± 2                                                                             84 ± 1.5                                    0.25%   5.0                                                                               5   5/5                                                                               -- -- 108 ± 22                                                                            99 ± 24                              Combinations                                                                    T/L   1/0.125 4.9                                                                               5.5 5/5                                                                               -- -- 309 ± 17                                                                            251 ± 51                              T/L   2/0.125 4.8                                                                               5.0 4/5                                                                               1/5                                                                               -- 316 ± 33                                                                            290 ± 46                              T/L   5/0.125 4.6                                                                               3.5 5/5                                                                               -- -- --      6<24 hrs.                                T/L   1/0.25  4.7                                                                               4.5 5/5                                                                               -- -- 5.5<24 hrs.                                                                            299 (2)                                  T/L   2/0.25  4.8                                                                               3.0 5/5                                                                               -- -- --      5.5<24 hrs.                              T/L   5/0.25  4.6                                                                               1.5 5/5                                                                               -- -- --      6<24 hrs.                               __________________________________________________________________________      NOTES: C = Complete block; P = Partial block; S = Slight effect; R.G. =        Recovery of grasping; C.R. = Complete Recovery; T = Tetrodotoxin; L =          Lidocaine. Durations are for complete blocks only. Onset times are             approximate. The pH's are after addition of epinephrine; all solutions         contained 1:100,000 epinephrine. Numbers of blocks are in specific             instances shown in parentheses.                                          

Table II: As in the first study, 1 μg/ml of tetrodotoxin produced no complete blocks; however, 2 μg/ml produced a complete block, with a duration of about 2 hours, in one out of five injections. The frequency of block with 3 μg/ml was only two out of five, but the block persisted for between 5 and 24 hours. In this study lower concentrations of lidocaine were used in order to ascertain whether or not the combinations show better frequencies than either tetrodotoxin or lidocaine alone.

                                      TABLE II                                     __________________________________________________________________________     RAT SCIATIC NERVE BLOCKS                                                                                      Duration (min.)                                        Concentration                                                                             Onset                                                                              Frequency                                                                               Mean ± S. D.                                    Compound                                                                            as Base                                                                               pH (min.)                                                                             C  P  S     C.R.  R.G.                                   __________________________________________________________________________     Tetrodotoxin                                                                          1 μg/ml                                                                             4.6                                                                               --  0/5                                                                               0/5                                                                               5/5                                                                               --       --                                            2 μg/ml                                                                             4.7                                                                               31  1/5                                                                               0/5                                                                               4/5                                                                               120      102                                           3 μg/ml                                                                             4.5                                                                               56  2/5                                                                               0/5                                                                               3/5                                                                               --       5<24 hrs.                              Lidocaine                                                                             0.05%   4.6                                                                               --  0/5                                                                               2/5                                                                               3/5                                                                               --       --                                            0.1%    4.6                                                                               43  2/5                                                                               2/5                                                                               1/5                                                                               58       44                                     Combinations                                                                    T/L   1/0.05  4.6                                                                               31  1/5                                                                               2/5                                                                               2/5                                                                               68       48                                      T/L   2/0.05  4.4                                                                               10  2/5                                                                               2/5                                                                               1/5                                                                               255      176                                     T/L   3/0.05  4.5                                                                               16  3/5                                                                               2/5                                                                               -- 6 1/2<24 hrs.                                                                           359 ± 42                             T/L   1/0.1   4.5                                                                               11  2/5                                                                               3/5                                                                               -- 144      93                                      T/L   2/0.1   4.6                                                                                6  4/5                                                                               0/5                                                                               1/5                                                                               242 ± 68                                                                             188 ± 83                             T/L   3/0.1   5.2                                                                               14  4/5                                                                               1/5                                                                               -- 304 (1)  317 ± 50                                                           6 1/2<24 hrs.                                                                           (3)                                    __________________________________________________________________________      See notes under Table I.                                                 

Table III: Tetrodotoxin at 3 μg/ml produced in three out of five animal blocks that lasted between 4 and 24 hours. In combinations with several local anesthetic agents, frequency was improved and onset times were shorter than with tetrodotoxin alone. All the combinations containing 1 μg/ml of tetrodotoxin exhibited durations of block much greater than obtained with the local anesthetic agents alone. The study clearly demonstrates that, in rat sciatic nerve blocks, the presence of concentrations of tetrodotoxin that by themselves are subthreshhold can cause marked increases in the durations of block of several local anesthetic agents.

                                      TABLE III                                    __________________________________________________________________________     RAT SCIATIC NERVE BLOCKS                                                                                      Duration (min.)                                        Concentration                                                                             Onset                                                                              Frequency                                                                               Mean ± S. D.                                   Compound                                                                             as base                                                                               pH (min.)                                                                             C. P  S     C.R.  R.G.                                   __________________________________________________________________________     Tetrodotoxin                                                                          1 μg/ml                                                                             4.6                                                                               --  0/5                                                                               1/5                                                                               4/5                                                                               --       --                                            3 μg/m.                                                                             4.3                                                                               48  3/5                                                                               2/5                                                                               -- 4<24 hrs.                                       Lidocaine                                                                             2.0%    4.4                                                                               2.0 5/5                                                                               -- -- 172 ± 17                                                                             160 ± 12                             T/L   1/2.0   4.5                                                                               1.5 5/5                                                                               -- -- 223(2)   188(2)                                                                4 1/2<24 hrs.                                                                           (3)                                     T/L   3/2.0   4.3                                                                               1.5 5/5                                                                               -- -- 4 1/2<24 hrs.                                   Bupivacaine                                                                           0.5%    5.0                                                                               2.5 5/5                                                                               -- -- 232 ± 39                                                                             183 ± 18                             T/B   1/0.5   5.2                                                                               6.0 5/5                                                                               -- -- 282 (2)  265 ± 45                                                           5<24 hrs. (3)                                    T/B   3/0.5   5.4                                                                               2.5 5/5                                                                               -- -- 5<24 hrs.                                       Prilocaine                                                                            2.0%    5.0                                                                               2.5 5/5                                                                               -- -- 153 ± 16                                                                             123 ± 6                              T/Pr  1/2.0   4.8                                                                               <1.0                                                                               5/5                                                                               -- -- 5<24 hrs.                                                                               251 ± 26                             T/Pr  3/2.0   4.8                                                                               2.0 5/5                                                                               -- -- 5<24 hrs.                                       Tetracaine                                                                            0.25%   5.2                                                                               4.0 3/5                                                                               2/5                                                                               -- 206(2)   180(2)                                                                4 1/2<24 hrs.                                                                           (1)                                     T/Tet 1/0.25  5.9                                                                               5.5 4/5                                                                               1/5                                                                               -- 4<24 hrs.                                        T/Tet 3/0.25  6.4                                                                               5.0 5/5                                                                               -- -- 3<24 hrs.                                       __________________________________________________________________________      See Notes under Table I.                                                       B = Bupivacaine; Pr = Prilocaine; Tet = Tetracaine.                      

EXAMPLE 2

The use of anesthetics of the present invention is also shown through peridural blocks in the cat. The surgical techniques and testing methods have been described in detail (Duce et al: Brit. J. Anaesth., Vol. 41, 579-587 (1969)). The animals were treated according to the following scheme in this study:

    ______________________________________                                         Cat  Weight    Day (treatment)                                                 No.  and Sex   1      2      3       4       5                                 ______________________________________                                         124  3.6 kg F  X      L      TTX     L/TTX   X                                 125  2.8 kg F  X      L      L/TTX   TTX     X                                 127  4.0 kg M  X      TTX    L       L/TTX   X                                 128  2.8 kg F  X      TTX    L/TTX   L       X                                 ______________________________________                                          X = XylocaineO.sup.R HCl, 2% as salt                                           L = Lidocaine HCl, 2% as base                                                  TTX = Tetrodotoxin, 1 μg/ml                                                 F = female                                                                     M = male                                                                 

All animals were tested with 2 percent Xylocaine (a commercial local anesthetic composition based on lidocaine as the active ingredient) on Days 1 and 5 to ascertain the stability of the peridural cat preparation. Within the test period, laboratory-prepared samples of lidocaine were used containing only lidocaine and epinephrine or lidocaine, epinephrine and tetrodotoxin in specified proportions. Solutions were freshly prepared each day of use; epinephrine was added and the pH taken shortly before administration. The pH's of the solutions were: tetrodotoxin, 4.5-6.75; lidocaine HCl, 4.75-4.8; lidocaine/tetrodotoxin, 4.75-4.9.

The results are summarized in Table IV. In general, no overt systemic effects were noted following administration of the test solutions. Animal No. 127 exhibited salivation and emesis, with bile present, about 3 hours and 45 minutes after administration of the lidocaine/tetrodotoxin combination. However, these observations were not considered significant.

Statistical analysis of the data showed that the Xylocaine® control values obtained on days 1 and 5 are not significantly different. Since tetrodotoxin alone produced no blocks, it as excluded from the analysis of variance in order to keep the variance reasonably homogeneous. A four-way analysis of variance was, therefore, done only with the data obtained with 2 percent lidocaine and with the lidocaine/tetrodotoxin combination. The durations of block with the lidocaine tetrodotoxin combination were statistically significantly longer than with lidocaine itself.

                                      TABLE IV                                     __________________________________________________________________________     PERIDURAL ANESTHESIA IN CAT                                                                Deep Motor Block                                                                               Block of Support of Weight                                                                     Block of Flexion Reflex            Compound and                                                                               Duration        Duration        Duration                           Concentration                                                                              x ± S.E.                                                                          Onset                                                                              Frequency                                                                            x ± S.E.                                                                          Onset                                                                              Frequency                                                                            x ± S.E.                                                                            Onset                                                                              Frequency              __________________________________________________________________________     2% XylocaineO .sup.R  (Day 1)                                                              119 ± 12                                                                          1   8/8   98 ± 13                                                                           <1  8/8   48 ± 10                                                                             8   4/8                    2% XylocaineO .sup.R  (Day 5)                                                              124 ± 11                                                                          1-2 8/8   106 ±  9                                                                          1   8/8   70 ± 17                                                                             7   6/8                    1 μg/ml Tetrodotoxin                                                                    --    --  0/8   --    --  0/8   --      --  0/8                    2% Lidocaine                                                                               115 ± 10                                                                          2-3 8/8   88 ±10                                                                            2   8/8   66 ± 19                                                                             7   5/8                    Lidocaine/tetrodotoxin                                                                     226 ±  9                                                                          <1  8/8   188 ±  9                                                                          <1  8/8   109 ±  8                                                                            7   7/8                    __________________________________________________________________________      Durations are in minutes.                                                      Mean onset times are approximate.                                               Durations of block of flexion reflex in this table were calculated            without zero values.                                                           All solutions contained 1:100,000 epinephrine.                           

EXAMPLE 3

The effectiveness of the local anesthetics of the present invention in the absence of epinephrine is shown by the data set forth in Tables V, VI and VII. The data summarized in these tables were obtained following the same procedures as described in Example 1.

Five separate studies were done, and a tetrodotoxin control group was run in each study. Frequency of block with tetrodotoxin ranged from 0/5 to 3/5, and durations ranged from about 180 to 240 minutes. Frequency of block was 5/5 with all combinations except that containing phenacaine (Table VI). The one partial block in this case may have been due to failure to inject the solution sufficiently close to the sciatic nerve trunk. The frequency of block with the diperodon-tetrodotoxin, cyclomethycaine-tetrodotoxin and dibucaine-tetrodotoxin were better than with diperodon, cyclomethycaine, dibucaine or tetrodotoxin by itself.

In all cases, the combinations produced durations markedly longer than obtained with the local anesthetics alone. The durations of tetrodotoxin alone were closer to those with the combinations; the frequencies were consistently lower than those produced by the combinations.

                                      TABLE V                                      __________________________________________________________________________     RAT SCIATIC NERVE BLOCKS                                                                                    Duration (min.)                                              % Conc. Onset                                                                              Frequency                                                                            Mean ± S. D.                                    Compound  as base                                                                             pH (min.)                                                                             C  P     C.R.                                                                              R.G.                                        __________________________________________________________________________     Lidocaine  2.0  4.8                                                                               1   5/5                                                                               -- 108 ± 48                                                                          103 ± 37                                 Lidocaine/TTX                                                                             2.0  4.8                                                                               <1  5/5                                                                               -- 385 ± 25                                                                          348 ± 17                                 Procaine   2.0  5.5                                                                               2.5 5/5                                                                               --  62 ± 7                                                                            60 ± 7                                  Procaine/TTX                                                                              2.0  5.5                                                                               2   5/5                                                                               -- 356 ± 53                                                                          314 ± 58                                 Chloroprocaine                                                                            2.0  5.4                                                                               1.5 5/5                                                                               -- 111 ± 65                                                                           87 ± 36                                 Chloroprocaine/TTX                                                                        2.0  5.3                                                                               1   5/5                                                                               -- 351 ± 73                                                                          325 ± 46                                 Tetrodotoxin                                                                              2μg/ml                                                                           6.0                                                                               13  2/5                                                                               0/5                                                                               242 ± 4                                                                           226± 5                                   Diperodon  0.25 5.4                                                                               22  2/5                                                                               0/5                                                                               124    64                                         Diperodon/TTX                                                                             0.25 5.4                                                                               9   5/5                                                                               -- 332 ± 59                                                                          286 ± 33                                 Propoxycaine                                                                              0.25 5.4                                                                               4   5/5                                                                               --  64 ±  12                                                                          52 ± 15                                 Propoxycaine/TTX                                                                          0.25 5.5                                                                               1.5 5/5                                                                               -- 262 ± 91                                                                          239 ± 102                                Hexylcaine 0.5  5.6                                                                               3   5/5                                                                               -- 112 ± 12                                                                           99 ± 17                                 Hexylcaine/TTX                                                                            0.5  5.5                                                                               4.5 5/5                                                                               -- 339 ± 17                                                                          303 ± 12                                 Cocaine    0.25 6.1                                                                               4.5 5/5                                                                               --  98 ± 9                                                                            86 ± 17                                 Cocaine/TTX                                                                               0.25 5.6                                                                               5   5/5                                                                               -- (1 day)                                                                              361 ± 28                                 Tetrodotoxin                                                                              2μg/ml                                                                           6.1                                                                               16  2/5                                                                               1/5                                                                               216 ± 51                                                                          161                                         __________________________________________________________________________      TTX = Tetrodotoxin, 2 μg/ml: C = Complete block; P = Partial block;         C.R. = Complete recovery of normal motor function; R.G. = Recovery of          grasping; Durations are for complete blocks only; Onset times are              approximate.                                                             

                                      TABLE VI                                     __________________________________________________________________________     RAT SCIATIC NERVE BLOCKS                                                                                  Duration (min.)                                               % Conc.                                                                               Onset                                                                              Frequency                                                                            Mean ± S. D.                                      Compound as base                                                                            pH (min.)                                                                             C  P     C.R.                                                                              R.G.                                          __________________________________________________________________________     Phenacaine                                                                               0.25                                                                               5.6                                                                               4.5 5/5                                                                               --  78 ± 32                                                                           70 ± 32                                   Phenacaine/TTX                                                                           0.25                                                                               5.5                                                                               8   4/5                                                                               1/5                                                                               282 ± 74                                                                          253 ± 71                                   Benoxinate                                                                               0.25                                                                               5.6                                                                               3   5/5                                                                               -- 116 ± 24                                                                           97 ± 20                                   Benoxinate/TTX                                                                           0.25                                                                               5.6                                                                               8   5/5                                                                               -- 320 ± 54                                                                          285 ± 58                                   Butacaine 0.25                                                                               5.8                                                                               6   4/5                                                                               1/5                                                                                73 ± 7                                                                            67 ± 2                                    Butacaine/TTX                                                                            0.25                                                                               5.6                                                                               5   5/5                                                                               -- 241 ± 24                                                                          204 ± 37                                   Tetrodotoxin                                                                             2 μg/ml                                                                         6.1                                                                               18  1/5                                                                               -- 181   150                                           Proparacaine                                                                             0.5 6.0                                                                               1.5 5/5                                                                               --  98 ± 20                                                                           89 ± 14*                                  Proparacaine/TTX                                                                         0.5 6.1                                                                               2   5/5                                                                               -- 429 ± 41                                                                          415 ± 50*                                  Tetrodotoxin                                                                             2μg/ml                                                                          6.2                                                                               13  3/5                                                                               2/5                                                                               222 ± 48                                                                          206 ± 42                                   __________________________________________________________________________      TTX = Tetrodotoxin, 2μg/ml; C = Complete block; P = Partial block; C.R      = Complete recovery of normal motor function R.G. = Recovery of grasping;      Durations are for complete blocks only; Onset times are approximate.           *Means of 3 animals; 2/5 died.                                           

                                      TABLE VII                                    __________________________________________________________________________     RAT SCIATIC NERVE BLOCKS                                                                                     Duration (min.)                                              % Conc. Onset                                                                              Frequency                                                                            Mean ± S. D.                                   Compound   as base                                                                             pH (min.)                                                                             C  P     C.R.                                                                              R.G.                                       __________________________________________________________________________     Cyclomethycaine                                                                            0.125                                                                               5.1                                                                               17  1/5                                                                               4/5                                                                               145   115                                        Cyclomethycaine/TTX                                                                        0.125                                                                               5.2                                                                               5   5/5                                                                               -- 273 ± 43                                                                          231 ± 41                                Dibucaine   0.125                                                                               5.4                                                                               6   3/5                                                                               1/5                                                                               125 ± 22                                                                          108 ± 25                                Dibucaine/TTX                                                                              0.125                                                                               5.4                                                                               6   5/5                                                                               -- 324 ± 47                                                                          272 ± 56                                Tetrodotoxin                                                                               2μg/ml                                                                           5.6                                                                               --  0.5                                                                               1/5                                                                               --    --                                         __________________________________________________________________________      TTX = Tetrodotoxin, 2μg/ml; C = Complete block; P = Partial block; C.R      = Complete recovery of normal motor function; R.G. = Recovery of grasping      Durations are for complete blocks only;                                        Onset times are approximate.                                             

EXAMPLE 4

The use of desoxytetrodotoxin was tested following the procedure described in Example 1. The desoxy derivative was substituted for the tetrodotoxin referred to in Example 1. Desoxytetrodotoxin was tested, without epinephrine, in rat sciatic nerve blocks. At concentrations of 5, 10 and 20 μg/ml it produced no blocks. The duration of block of a combination containing 2 percent lidocaine and 5 μg/ml of desoxytetrodotoxin was not significantly different from that of 2 percent lidocaine alone. However, combinations containing 10 and 20 μg/ml of desoxytetrodotoxin produced blocks that were significantly longer (1.4-1.6 times) than that of lidocaine alone (0.008 > p > 0.016).

This result is to be expected based on the tests of tetrodotoxin in view of the lower activity shown by the desoxy derivative in toxicity tests. Literature on the toxicity of tetrodotoxin and its desoxy derivative reports the latter to be between one quarter and one tenth as toxic as its parent toxin.

EXAMPLE 5

Method: Mature male beagles are surgically prepared by implantation of a cannula into a lumbar vertebra so that drug solutions may be administered into the peridural space. After administration of local anesthetic solutions, the animals are examined at intervals for duration of loss of pain in the scrotal area and in the digits of the hind limbs as well as for loss of ability to support their weight.

Response to and awareness of pain stimuli in scrotal areas is a test for anesthetic block in spinal roots L3-4 and Sl-2-3. These roots are the furthest removed from the point of injection (L6) and, therefore, least likely to be affected by the anesthetic. Return of response to pain in the scrotum is often the first sign of recovery and indicates recession of anesthesia to at least L4 anteriorly and S2 posteriorly.

                                      TABLE VIII                                   __________________________________________________________________________     PERIDURAL ANESTHESIA IN DOGS                                                           Onset: mean and range                                                                         Duration: mean and range                                Compound and                                                                           Digital                                                                             Scrotal                                                                             Weight                                                                              Digital                                                                             Scrotal                                                                             Weight                                        Concentration                                                                          Pain Pain Support                                                                             Pain Pain Support                                       __________________________________________________________________________     Lidocaine 2%                                                                           7    8    <5   127  111  137                                            (n=3)                 76-162                                                                              62-152                                                                              108-162                                       Tetrodotoxin                                                                           19.5 15*  <17  225       406                                            4 μg/ml                                                                     (n=2)  19-20          87-350                                                                              0-125                                                                               339-473                                       Lidocaine 2%           316  301  462                                           Tetrodotoxin                                                                           <5   <5   <3   245-387                                                                             235-367                                                                             400-525                                        4 μg/ml                                                                     (n=2)                                                                         __________________________________________________________________________      *One animal only; no anesthesia in second animal.                              Onsets and durations are in minutes.                                           All Solutions contained 1:100,000 epinephrine.                                 Volume of administration = 5 ml.                                               n = number of animals                                                          NOTE:                                                                          (1) With lidocaine onset is rapid, frequency of block is 100%, but             durations are short.                                                           (2) With tetrodotoxin durations are long, but onset is slow and frequency      of block of scrotal pain is poor.                                              (3) With the combination onset is rapid, frequency is 100% and durations       are long.                                                                

EXAMPLE 6

Following the method described in Example 1 above, various local anesthetic compounds alone, TTX alone and combinations of the compounds with TTX were tested for their ability to block the rat sciatic nerve. TTX was used uniformly in the amount of 2 μg/ml. Each of the compositions tested contained epinephrine in concentration of 1:100,000. The results are presented in Table IX. In the case of compound A in 0.5% concentration, duration was about 126 minutes. TTX alone was about 295 minutes but frequency was not good. In combination, frequency was good and duration was greater than 420 minutes.

In the case of compound D at 0.25% concentration, duration was about 128 minutes alone but greater than 420 minutes in combination with TTX. In the case of compound E at 0.25% concentration, no blocks were observed alone, but in combination with TTX the duration was about 148 minutes. In the case of compound F alone at 0.125% concentration, duration was only 78 minutes with poor frequency, whereas in combination with TTX duration was greater than 322 minutes and frequency had improved. For compound G at 0.5% concentration, duration was 104 minutes alone and about 286 minutes in combination with TTX.

It should be noted moreover that in the case of TTX alone, the frequency and duration were quite variable ranging from zero frequency to 4 out of 5, and ranging from zero duration to 295 minutes or more.

                  Table IX                                                         ______________________________________                                         Rat Sciatic Nerve Blocks                                                       Tetrodotoxin (TTX) (2 μg/ml) and Various Local Anaesthetic                  Compounds. Epinephrine concentration 1:100,000.                                                            Duration (min.)                                    Compound       Frequency    Mean ± S.D.                                     ______________________________________                                         TTX            2/5          295*                                               A (0.5%)       5/5          126 ± 12                                        TTX + A (0.5%) 5/5          >420, <24 hrs.**                                   A (1.0%)       5/5          157 ± 18                                        TTX + A (1.0%) 5/5          >420, <24 hrs.                                     TTX            4/5          316 ± 10*                                       D (0.25%)      5/5          128 ± 13                                        TTX + D (0.25%)                                                                               5/5          >420, <24 hrs.                                     D (0.5%)       5/5          133 ± 7                                         TTX + D (0.5%) 5/5          >420, <24 hrs.                                     TTX            0/6          0                                                  E (0.25%)      0/6          0                                                  TTX + E (0.25%)                                                                               4/6          148 ± 27                                        TTX            0/5          0                                                  F (0.125%)     1/5          78                                                 TTX + F(0.125%)                                                                               3/5          >322 min.                                          TTX            0/5          0                                                  G (0.5%)       5/5          104 ± 14                                        TTX + G (0.5%) 4/5          286 ± 197                                       ______________________________________                                           * One animal blocked >420 min.                                                ** >420, <24 hrs. means that the animals returned to normal during a           period when they were not observed, this period being longer than 7 hrs.       and shorter than 24 hrs.                                                 

EXAMPLE 7

In vitro tests were made on the isolated intact frog sciatic nerve using compounds B, C and lidocaine alone and in combination with TTX. The results and the method followed are presented in Table X. The reduction in the action potential of compound B alone was 22% and for TTX alone it was 15%, as compared with a reduction of 94% for the combination. For compound C alone the reduction was 24%, and for TTX alone 29%. whereas the combination again reduced the potential by 94%. For lidocaine and TTX each alone the reductions were 15% and 7%, respectively, as compared with a reduction of 61% for the combination of the two.

                  Table X                                                          ______________________________________                                         Block of Isolated Intact Frog Sciatic Nerve.                                   ______________________________________                                                                  Percent reduction                                                                          Number of                                                          of the action                                                                              ex-                                                       Concn.   potential.  peri-                                     Compound pH     mM       Mean and range                                                                             ments                                     ______________________________________                                         B        5.6    0.625    22 (10-38)  16                                        TTX      5.6    3.10.sup.-.sup.4                                                                        15 ( 8-)    17                                        B + TTX  5.6    as above 94 (80-100) 17                                        C        5.6    0.156    24 (15-52)  8                                         TTX      5.6    3.10.sup.-.sup.4                                                                        29 (14-80*) 6                                         C + TTX  5.6    as above 94 (78-100) 12                                        Lidocaine                                                                               7.0    0.625    15 (6-30)   6                                         TTX      7.0    1.10.sup.-.sup.4                                                                         7 (2-12)   6                                         Lidocaine)                                                                     )        7.0    as above 61 (20-100) 12                                        + TTX)                                                                         ______________________________________                                          *Occasionally a high value is observed, probably caused by a minute damag      to the nerve sheath during dissection. It takes about 50 times the             concentration of TTX which is necessary to block a desheathed nerve in         order to obtain the same degree of block of an intact (sheathed) nerve.        as

Method: The method is essentially is described by A. P. Truant, Arch. Int. Pharmacodyn. 115, 483-497 (1958).

Sciatic nerve trunks of Rana pipiens are prepared by dissecting the nerve from its roots in the spinal cord to the ankle and placing it on silver-silver chloride electrodes so that stimulation and recording of the action potential can be performed during the course of application of the test compounds and during the recovery period. The bathing solution is Tasaki Ringer's. The observations lasted for 40 minutes allowing the action potentials to reach essentially a stable value (equilibrium).

EXAMPLE 8

Using the procedure described in Example 1 above, the effect of several known vasoconstrictors on rat sciatic nerve blocks was investigated using lidocaine (0.125%) and tetrodotoxin (2 μg/ml) in combination. The results are given in Table XI. Without any vasoconstrictors, the frequency was very poor and the duration of block was 174 minutes. With phenylephrine, levonordefrin, or epinephrine, however, frequency was greatly improved and duration had about doubled.

                  Table XI                                                         ______________________________________                                         Effect of Vasoconstrictors on Rat Sciatic Nerve Blocks                         Obtained with Lidocaine (0.125%) and Tetrodotoxin (2 μg/ml).                                                 Duration of                                                                    Block (min.)                                  Vasoconstrictor                                                                           Concn.     Frequency  Mean ± S. D.                               ______________________________________                                         None       --         1/5        174                                           Phenylephrine                                                                             1:20,000   5/5        377 ± 27                                   Levonordefrin                                                                             1:20,000   5/5        354 ± 12                                   Epinephrine                                                                               1:200,000  5/5        368 ± 24                                   ______________________________________                                    

EXAMPLE 8a

Using the procedure described in Example 1, except that no epinephrine was added to the solutions tested, the local anesthetics falicain and pramoxine were tested for blockage on the rat sciatic nerve alone and in combination with TTX at 2 μg/ml. The results are presented in the following Table XII.

                  TABLE XII                                                        ______________________________________                                         Rat Sciatic Nerve Blocks                                                                       Frequency  Duration                                            ______________________________________                                         0.25% falicain    5/5          55 ± 22                                      0.25% falicain                                                                 ± TTX, 2 μg/ml                                                                             5/5          116 ± 71                                     0.25% pramoxine   0/5          0                                               0.25% pramoxine                                                                ± TTX, μg/ml                                                                               2/5          190 ± 76                                     TTX, 2 μg/ml   0.5          0                                               ______________________________________                                    

It will be observed that the ingredients were tested at dose level that did not result in any anesthesia at all for two of them, and only 55 min. for the third one, whereas the combination gave anesthesia about 2 to 3 hrs. The frequency of complete block was raised from 0 to 40% in the case of pramoxine.

Compounds A, B, C, D and L described in Table A above are made by the procedure described in U.S. patent application Ser. No. 369,146, filed June 12, 1973, which is a continuation-in-part of Ser. No. 325,378, filed January 22, 1973, now abandoned, both assigned to the same assignee as the present application, which disclosure is incorporated herein by reference.

The method of preparing compounds S and T is disclosed in U.S. patent application Ser. No. 164,022 filed July 19, 1971, now U.S. Pat. No. 3,812,147, which is incorporated herein by reference.

The method of preparing compound Q is disclosed in U.S. patent application Ser. No. 321,590 filed January 8, 1973, now abandoned, which is incorporated herein by reference.

Compounds H, J and M and mepivacaine are known compounds disclosed in the published literature.

EXAMPLE 9 Synthesis of 2-(N-ethyl-isopropylamino)-2',6'-propionoxylidide (Compound E)

A mixture of 12.81 g (0.050 mole) of 2-bromo-2',6' -propionoxylidide, 11.31 g (0.130 mole) ethyl-isopropylamine and 30 ml dry toluene was heated in a glass-lined, stainless-steel pressure vessel at 105° for 20 hours. After cooling to 25°, the brown reaction mixture was filtered, extracted three times with a total of 50 ml of 3 N HCl. The aqueous solution was heated to 75° for ten minutes with decolorizing carbon and then filtered. To the chilled solution was added 10 ml concentrated NH₃. The product which precipitated was filtered, washed, and dried. Yield: 6.93 g (52.9%) m.p. 50-2°.

Anhydrous ethereal HCl was added to 6.90 g of the above base dissolved in 100 ml dry ether until the solution was acidic to moist pH paper, giving 6.15 g of tacky brown material, m.p. 191°-201°. The hydrochloride was recrystallized from a mixture of butanone and alcohol. Yield: 6.02 g, m.p. 207.5° - 209°.

Analysis: Calc'd. for C₁₆ H₂₇ ClN₂ O: C 64.30, H 9.11, N 9.37, Cl 11.86. Found: C 64.16; H 9.16, N 9.49, Cl 12.09.

EXAMPLE 10

A. Synthesis of 2-Bromo-4'-butoxy-2',6'-dimethyl propionanilide

To a chilled (ca 10° ) solution of 50.7 g (0.263 mole) of 4-butoxy-2,6-dimethylaniline [Buchi et al., Helv. Chim. Acta, 34, 278 (1951)] in 224 ml glacial acetic acid was added rapidly 62.4 g (.289 mole) of 2-bromo-propionyl bromide and immediately thereafter a chilled (ca 5° ) solution of 87.2 g sodium acetate trihydrate in 362 ml water. This mixture was shaken for 1/2 hour, filtered, washed with water until the washes were neutral, and dried in vacuo over silica gel and KOH; yield 68.9 g (71.6%); m.p. 132.5° - 133.5°. The product was recrystallized from 95% ethanol; m.p. 135.5° - 136°.

Analysis: Calc'd for C₁₅ H₂₂ NO₂ Br : C 54.87, H 6.76, Br 24.34. Found:C55.06, H 6.22, Br 24.69.

B. Synthesis of 2-Methylamino-4'-butoxy-2',6'-dimethyl-propionanilide (Compound F)

To a cold stirred solution of 14.8 g. of monomethyl amine in 250 ml dry benzene was added (portionwise, keeping temperature below 10° ) 19.5 g (0.0594 mole) of 2-bromo-4'-butoxy-2',6'-dimethyl propionanilide (made according to the procedure in the first part of this example); this dissolved readily forming a clear solution. The mixture was heated to 70° for ca 1 hr. with stirring, at which point a white precipitate had separated and reflux became so vigorous that the reaction had to be controlled by external cooling.

The precipitated methylammonium bromide was filtered off. Excess amine and solvent were removed in vacuo from the filtrate, giving a white residue which was dissolved in 120 ml 0.5 M HCl and filtered. The filtrate was extracted with 3 × 25 ml. ether; and the ether extracts discarded.

The aqueous phase was alkalized to pH 11, and extracted with ether; the combined extracts were dried (Na₂ SO₄), filtered, and evaporated, giving a yield of 8.7 g (52.7%); m.p. 107°-107.5°. Recrystallization from cyclohexane did not affect the melting point.

Analysis: Calc'd. for C₁₆ H₂₆ N₂ O₂ : C 69.0; H 9.41; N 10.06. Found: C 69.0; H 9.17; N 10.06.

EXAMPLE 11 Synthesis of 2-(N-Methyl-n-propylamino)-2',6'-butyroxylidide (Compound G)

To a stirred solution of N-methyl-n-propylamine (9.10 g, 0.125 mole) in 175 ml of anhydrous benzene was added 2-iodo-butyro-2',6'-xylidide (13.2 g, 0.0415 mole). The mixture was allowed to reflux for 5 hrs.

The reaction mixture was extracted with 1 M HCl. After filtration to remove trace insolubles, the pH was adjusted to 9 with 7 M NaOH, which caused the formation of a light-yellow waxy solid. The latter was filtered, washed with water, and dried; yield 4.00 g (36.7%).

This base was converted to the hydrochloride salt with ethereal HCl. The hydrochloride was twice-recrystallized from ethanol/ether, affording crystals melting at 214°-215° C.

Analysis: Calc'd. for C₁₆ H₂₇ ClN₂ O : C 64.3; H9.11; Cl 11.86. Found: C 64.4; H 9.01; Cl 11.80.

EXAMPLE 12 Synthesis of 2-Cyclobutylamino-2',6'-acetoxylidide (Compound K).

To a solution of cyclobutylamine (39.8 g) in 600 ml benzene was added 2-chloro-2',6'-acetoxylidide (49.4 g), slowly, with stirring, and the mixture was refluxed for about 5 hrs. After cooling, the mixture was filtered to remove the cyclobutylammonium chloride formed. The filtrate was stripped of solvent and excess amine in vacuo; leaving a crude residue.

The residue was dissolved in 0.5 M hydrochloric acid, the solution was made alkaline with sodium hydroxide solution and the base was extracted carefully with ether. The ether solution was dried (Na₂ SO₄), the ether and low-boiling components were evaporated in vacuo at 40°-50° C. and the residue converted to a hydrochloride by addition of ethereal hydrogen chloride to its filtered ether solution. From the hydrochloride the base was obtained by dissolution in water, addition of sodium hydroxide solution to alkaline pH, extraction with ether, drying of the ether extract (Na₂ SO₄), filtering, and evaporation of the ether. The base could be recrystallized from cyclohexane, petroleum ether (b.p. 60°-110° C.), or heptane. The melting point was found to be 75°-78° C.

Analysis: Calc'd. for C₁₄ H₂₀ N₂ O : C 72.4, H 8.68, N 12.06. Found: C 72.4, H 8.88, N 11.93.

EXAMPLE 13 A. Synthesis of 2-(sec-butylamino)-2',6'-acetoxylidide

To a solution of 62.2 g of sec-butylamine in 500 ml benzene was added slowly 41.5 g of 2-chloro-2',6'-acetoxylidide. The mixture was heated to reflux for seven hours and allowed to cool overnight. The precipitate of sec-butyl amine hydrochloride that formed was filtered off and the filtrate was evaporated to an oily residue. The residue was dissolved in ether, and the solution was filtered, dried (Na₂ SO₄), and evaporated to an oily residue (45.7 g). This crude product was distilled under vacuum, giving an oily liquid that solidified when chilled. Yield: 38.5 g (78%); b.p. 146°/0.05 mm; m.p. 44.5°-45.5°.

Analysis: Calc'd. for C₁₄ H₂₂ N₂ O : C 71.75, H 9.46, N 11.96. Found: C 71.99, H 9.35, N 12.12. The hydrochloride melted at 176.5 - 178.5°. ##STR5##

B. Synthesis of 2-(N-ethyl-sec-butylamino)-2',6'-acetoxylidide (Compound P)

To 140 g of diethyl sulfate was added 30.5 g of 2-(sec-butylamino)-2',6'-acetoxylidide (made by the method described in the first part of this example). The mixture was heated to 100°-110° for five hours and cooled. Water and 5 N HCl were added to pH 2, forming a second phase. After stirring, the aqueous phase (pH 2) was separated, washed with two 100 ml portions of ether and brought up to pH 9 with concentrated NH₃. The basic aqueous phase was extracted with five 100 ml portions of ether. The solvent was stripped in vacuo from the combined ether phases, leaving a solidifying oil which was dissolved in ether, dried (Na₂ SO₄), filtered, and evaporated in vacuo. Yield: 26.2 g (76.8%); m.p. 50.5° - 54.5°. The product was twice distilled under high vacuum : b.p. 147°/0.025 mm; 165°/0.4 mm. Yield of redistilled product: 21.4 g (62.7%).

Analysis: Calc'd. for C₁₆ H₂₆ N₂ O : C 73.23%, H 9.99%, N 10.68%. Found: C 73.06%, H 9.66%, N 10.47%. 

We claim:
 1. An injectable local anesthetic composition having long-lasting local anesthetic effect which is a solution consisting essentially of a pharmaceutically acceptable carrier having dissolved thereina. an aminoalkyl benzoate local anesthetic compound in a concentration of from 0.05% to 5% by weight of the carrier and b. a toxin selected from the group consisting of from 0.5 to 10 micrograms of tetrodotoxin per milliliter of the carrier and from 10 to 20 micrograms of desoxytetrodotoxin per milliliter of the carrier.
 2. The composition as defined by claim 1 wherein said component (b) is tetrodotoxin.
 3. The composition as defined by claim 1 wherein said component (b) is desoxytetrodotoxin.
 4. The composition as defined by claim 2 wherein the aminoalkyl benzoate is procaine.
 5. The composition as defined by claim 2 wherein the aminoalkyl benzoate is chloroprocaine.
 6. The composition as defined by claim 2 wherein the aminoalkyl benzoate is tetracaine.
 7. The composition as defined by claim 2 wherein the aminoalkyl benzoate is propoxycaine.
 8. The composition as defined by claim 2 wherein the aminoalkyl benzoate is hexylcaine.
 9. The composition as defined by claim 2 wherein the aminoalkyl benzoate is cyclomethycaine.
 10. The composition as defined by claim 2 wherein the aminoalkyl benzoate is benoxinate.
 11. The composition as defined by claim 2 wherein the aminoalkyl benzoate is butacaine.
 12. The composition as defined by claim 2 wherein the aminoalkyl benzoate is proparacaine.
 13. The composition as defined by claim 1 which further contains an effective amount of a vaso-constrictor.
 14. A method of inducing anesthesia in mammals comprising administering to the mammal to be anesthetized an effective amount of an injectable local anesthetic composition having long-lasting local anesthetic effect which is a solution consisting essentially of a pharmaceutically acceptable carrier having dissolved thereina. an aminoalkyl benzoate local anesthetic compound in a concentration of from 0.05% to 5% by weight of the carrier and b. a toxin selected from the group consisting of from 0.5 to 10 micrograms of tetrodotoxin per milliliter of the carrier and from 10 to 20 micrograms of desoxytetrodotoxin per milliliter of the carrier.
 15. The method as defined by claim 14 wherein said component (b) is tetrodotoxin.
 16. The method as defined by claim 14 wherein said component (b) is desoxytetrodotoxin.
 17. The method as defined by claim 15 wherein the aminoalkyl benzoate is procaine.
 18. The method as defined by claim 15 wherein the aminoalkyl benzoate is chloroprocaine.
 19. The method as defined by claim 15 wherein the aminoalkyl benzoate is tetracaine.
 20. The method as defined by claim 15 wherein the aminoalkyl benzoate is propoxycaine.
 21. The method as defined by claim 15 wherein the aminoalkyl benzoate is hexylcaine.
 22. The method as defined by claim 15 wherein the aminoalkyl benzoate is cyclomethycaine.
 23. The method as defined by claim 15 wherein the aminoalkyl benzoate is benoxinate.
 24. The method as defined by claim 15 wherein the aminoalkyl benzoate is butacaine.
 25. The method as defined by claim 15 wherein the aminoalkyl benzoate is proparacaine.
 26. The method as defined by claim 14 wherein said composition further contains an effective amount of a vasoconstrictor. 